The present invention relates to the constitution of an ink tank of an ink jet printer, and particularly to the ink storage and ink feeding in an ink tank.
An ink jet printer has had the defect that the performance and quality of printing changes remarkably according to the printing posture, because it uses a liquid ink. Accordingly, a method has been devised which comprises modifying the flow of ink in an ink tank by the capillary action phenomenon and surface tension by putting fibers into the ink tank and correcting the deterioration of the characteristics due to the printing posture.
Hereunder, a conventional method is described according to FIG. 9. Ink 5 is fed to an ink jet printer 1 via an ink fed passage 2 from an ink tank 3. At this time, fibers 4 are put into the ink tank 3 and air is introduced into a space 7 from which ink among the fibers 4 is sucked out through an air intake 6. In this case, if the suction power of the ink jet printer 1 is strong, the ink 5 in the ink tank 3 is sucked to the side of the ink feed passage 2. But if lacking in suction power, however, it is impossible to sufficiently feed ink due to surface tension 20. In addition, if the level of the ink 5 in the ink tank 3 is lower than the nozzle of the ink jet printer 1, the ink jet printer will run out of ink.
Hence, the ink jet printer discloses in Japanese Patent Publication No. 11152/1988 uses ink usefully by collecting ink in the ink tank on the side of the ink feed passage, and at the same time prevents ink from spouting by transferring cells in the ink tank to the side of the space in the ink tank.
The ink jet printer disclosed in Japanese Patent Publication No. 11152/1988 is shown in FIG. 10. An ink jet head 1 is connected with an ink tank 3 via an ink feed passage 2. The internal diameter of the ink tank 3 becomes smaller as it approaches the side of the ink feed passage 2. One kind of fiber 4 is provided in the ink tank 3, and the density of the fiber 4 increases continuously as it approaches the side of the ink feed passage 2, because there is neither a cut-off nor a joint, and ink is collected to one side. Air is introduced into the space 7, from which ink is sucked out from an air intake 6. The air intake 6 is covered with a cover 8 when not used.
According to the conventional constitution, however, it is hard to design a fitting place in fitting an ink tank in a carriage. Ink cannot be introduced into the ink tank, and a sufficient amount of ink cannot be kept in the ink tank, not only because the shape is thin, but also because the fiber is gradually compressed. Consequently, there is a problem in that an ink tank must be large.
Moreover, when only ink is introduced into a vessel, it leaks according to changes of atmospheric temperature and pressure, and hence, in a cartridge-type ink tank to be used in various forms of ink jet printers, various constitutions and methods are employed for the purpose of preventing the leakage of ink and surely bestowing a certain back pressure upon a printing head.
For this, a method has been proposed in which an ink support material (urethane foam) in the vessel is impregnated with ink to maintain ink according to the capillary tube power of the support material, and the back pressure in the vessel is adjusted to an appropriate negative pressure (see e.g. Japanese Patent publication No. 87242/1988).
According to the above constitution, however, the storage volume of ink is reduced by the volume of the ink support material, and besides, ink cannot be usefully used up due to the capillary tube power of the ink support material.
Hence, as shown in FIG. 11, a longitudinally arranged constitution is proposed, in which an ink vessel 33 is divided into two rooms, namely, a main ink storage part 35 for storing ink alone and a secondary ink storage part 34 adjusting overflowed ink (see Japanese Patent publication No. 522/1990). In this constitution, an ink flow path 38 is set between the main ink storage part 35 and the secondary ink storage part 34 and a porous material is installed between a printing head support part 36 for supporting a printing head 39, the ink flow path 38 and the secondary ink storeroom 34.
According to this constitution, however, since the secondary ink storeroom 34, adjusting overflowed ink, does not open to the atmosphere, ink is kept in the secondary ink storeroom without a printing operation when a temperature change occurs. At this time, the diameter of droplets changes according to the occurrence of the difference of water columns between the printing head 39 and the secondary ink storeroom 34 and hence the change of the back pressure upon the printing head, there is a fear of ink leakage from the ink jet nozzle and it is difficult to adjust the back pressure.
Another conventional example of dividing an ink room into two rooms is the one shown in FIG. 12 (see also Japanese Patent Publication No. 99631/1975). In this example, a liquid well 40 is one ink room and is filled with foamed plastic 41 impregnated with ink. A feed pocket 46 for feeding ink into a printing head is at the lowest part. In a liquid fill device 42 provided as another ink room, is an air hole 43 at upper part, the inside is filled with ink 44 and a wick 45 is dipped therein. A tip 47 of the wick passes through an outer wall of the liquid fill device 42 and an opening 48 on an outer wall of the liquid well 40 and comes into contact with the foamed plastic 41 to feed ink.
According to the above constitution, however, there is a problem in ink storage, because the liquid fill device has an air hole. Since the liquid well is filled with the foamed plastic impregnated with ink, ink cannot be usefully used up owing to the capillary tube power. The back pressure increases with the decrease of ink, and thus it is difficult to adjust the back pressure.